What is causing a "whirring" sound on my MkV Volkswagen Golf?

I've owned a January 2005 Mark V Volkswagen Golf 1.9 TDI SE with 40,000 miles on the clock from new. Usually at the start of a journey I am sometimes aware of a very faint "whirring" type of sound that seems to be associated with normal acceleration. I mentioned this to a Golf Mark 4 TDI owner who said: "what you are hearing is quite normal". Is that correct? And what actually causes the very faint (difficult to describe) sound?
Might be the alternator. But when did you last have the timing belt changed? Usually a whirring is the first sign of the tensioner bearing starting to fail.
Answered by Honest John on

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